Effects of experimental warming on plant reproductive phenology in Xizang alpine meadow北大核心CSCD

Aims: Climate warming strongly influences reproductive phenology of plants in alpine and arctic ecosystems. Here we focus on phenological shifts caused by warming in a typical alpine meadow on the Qinghai-Xizang Plateau. Our objective was to explore phenological responses of alpine plant species to experimental warming. Methods: Passive warming was achieved using open-top chambers (OTCs). The treatments included control (C), and four levels of warming (T1, T2, T3, T4). We selected Kobresia pygmaea, Potentilla saundersiana, Potentilla cuneata, Stipa purpurea, Festuca coelestis and Youngia simulatrix as the focal species. Plant phenology was scored every 3-5 days in the growing season. The reproductive phenology phases of each species were estimated through fitting the phenological scores to the Richards function. Important findings: Under soil water stress caused by warming, most plants in the alpine meadow advanced or delayed their reproductive events. As a result, warming significantly delayed phenological development of K. pygmaea. Warming significantly advanced reproductive phenology of P. saundersiana, S. purpurea and F. coelestis, but not of P. cuneata and Y. simulatrix. In addition, warming significantly shortened the average flowering duration of alpine plant species. The potentially warmer and drier growing seasons under climate change may shift the reproductive phenology of the alpine systems in similar pattern.     

Effects of experimental warming on plant reproductive phenology in Xizang alpine meadow

Aims Climate warming strongly influences reproductive phenology of plants in alpine and arctic ecosystems. Here we focus on phenological shifts caused by warming in a typical alpine meadow on the Qinghai-Xizang Plateau. Our objective was to explore phenological responses of alpine plant species to experimental warming. Methods Passive warming was achieved using open-top chambers (OTCs). The treatments included control (C), and four levels of warming (T1, T2, T3, T4). We selected Kobresia pygmaea, Potentilla saundersiana, Potentilla cuneata, Stipa purpurea, Festuca coelestis and Youngia simulatrix as the focal species. Plant phenology was scored every 3-5 days in the growing season. The reproductive phenology phases of each species were estimated through fitting the phenological scores to the Richards function. Important findings Under soil water stress caused by warming, most plants in the alpine meadow advanced or delayed their reproductive events. As a result, warming significantly delayed phenological development of K. pygmaea. Warming significantly advanced reproductive phenology of P. saundersiana, S. purpurea and F. coelestis, but not of P. cuneata and Y. simulatrix. In addition, warming significantly shortened the average flowering duration of alpine plant species. The potentially warmer and drier growing seasons under climate change may shift the reproductive phenology of the alpine systems in similar pattern.     

实验增温对藏北高寒草甸植物繁殖物候的影响

全球气候变暖对高寒和极地地区的植物物候产生强烈的影响。该研究主要关注增温条件下藏北高寒草甸不同功能型植物繁殖时间(生殖物候)的改变。实验采用开顶箱式增温方法, 对3个主要功能群浅根-早花、浅根-中花和深根-晚花植物的现蕾、开花、结实时间进行观测。研究结果表明: (1)增温导致了土壤水分胁迫, 显著推迟了浅根-早花植物高山嵩草(Kobresia pygmaea)的繁殖时间; (2)增温显著提前了浅根-中花植物钉柱委陵菜(Potentilla saundersiana)和深根晚花植物紫花针茅(Stipa purpurea)和矮羊茅(Festuca coelestis)的繁殖时间; (3)增温没有显著影响浅根-中花植物楔叶委陵菜(Potentilla cuneata)和深根-晚花植物无茎黄鹌菜(Youngia simulatrix)的繁殖时间; (4)增温缩短了3种类型植物的开花持续时间。这些结果显示增温改变了藏北高寒草甸群落中多数物种的繁殖时间, 这预示着在未来更热更干的生长季, 青藏高原高寒草甸系统的植物物候格局可能会被重塑。     

Different temperature perception in high‐elevation plants: new insight into phenological development and implications for climate change in the alpine tundra

In alpine habitats, predicted warmer and longer growing seasons will influence plant phenology, with important implications for species adaptation and vegetation dynamics. However, little is known on the temperature sensitivity of different phenophases and on the characteristics allowing phenological variation among and within species. By integrating interannual micro‐climatic variability with experimental warming, we explored how the phenology of three alpine species is influenced by temperature and what mechanisms underlie intra‐ and inter‐specific phenological differences. The present study demonstrated that alpine plants have different temperature responses during their reproductive cycle, do not have constant thermal thresholds and heat‐use efficiencies to achieve the seed dispersal stage and can change their temperature sensitivity to flower along snowmelt gradients. In addition, the length of the reproductive cycle, which proved to be species‐specific under experimental warming, does not seem to be the only life‐history trait under selective pressure due to the short‐length of the snow‐free period. In a warming climate scenario, the phenology of sexual reproduction will be considerably altered, and alpine plants may be subjected to changes in population dynamics driven by altered perception of environmental cues appropriate for coordinating the timing of key life‐history events.     

Effects of simulated climate change on phenology and life history traits in Carex bigelowii

Climate change may have large effects on plants, especially in the Arctic. At two different sites, we studied the effects of enhanced temperature by using open-top chambers (OTCs) on the clonal sedge Carex bigelowii , a common plant in arctic and alpine tundra. At the subarctic-alpine site Latnjajaure, northern Sweden, overall flowering phenology was accelerated by open-top chambers (OTCs) during the five years of treatment. For this protogynous population, male flower phenology accelerated more than female flower phenology, which resulted in an increased gender phase overlap. Sexual reproductive effort at the ramet-level increased, both in male and female functions. Smut fungus incidence was not different among treatments, but a Dipteran seed predator attacked more ramets in the OTCs in one of five years. However, neither the fungus nor the seed predators affected plant growth or seed set measurably. Ramet-level growth increased in the OTCs at Latnjajaure, but decreased in the OTCs at the maritime subarctic site Thingvellir, Iceland after three years of treatment. At Latnjajaure, the initial ramet- level responses were still evident after five years, while responses at the ramet population level disappeared: there was no difference in flowering frequency of ramets in the fifth year of the warming treatment. This is interpreted as either meristem limitation or internal resource depletion. At Thingvellir flowering frequency was unaffected by warming treatment, while ramet production decreased. Ramet production was unaffected by the treatment at Latnjajaure. These site differences in responses could be the consequences of differences in climate or site specific conditions. The trade-off (negative correlation) between the number and size of vegetative offspring at Latnjajaure disappeared under enhanced temperatures (within the OTCs). This trade-off was not apparent under the warmer conditions at Thingvellir.     

Ranunculus glacialis L.: successful reproduction at the altitudinal limits of higher plant life

Biodiversity decreases with increasing altitude, mainly because of the increasingly adverse climate. In the European Alps, only a few plant species occur above 4,000 m a.s.l., among these is Ranunculus glacialis L. Current studies have shown that R. glacialis has a highly conservative growth strategy and low developmental plasticity in response to different dates of snowmelt. Therefore, it was of particular interest to observe whether this strategy is maintained at higher altitudes and to reveal the reproductive limits. We examined the effect of the date of snowmelt on reproductive development and reproductive success in R. glacialis over several years at two subnival sites (2,650 and 2,880 m a.s.l.) and at a nival site (3,440 m a.s.l.) in the Austrian Alps. At the subnival sites, reproductive performance was relatively stable (prefloration period, i.e. snowmelt to onset of anthesis, 2–3 weeks; postfloration period, i.e. onset of anthesis until fruit maturity, 4–5 weeks). Depending on the date of flowering, the mean seed/ovule (S/O) ratio was 0.5–0.8. The temporal safety margin between seed maturation and the onset of winter conditions was at least 1 month. The situation was quite different in the nival zone: the prefloration period usually lasted 1 month, anthesis up to 2 weeks, and seed development 6–7 weeks; when seeds matured in time, the S/O ratio was 0.4–0.6. Overall, R. glacialis shows a high developmental plasticity. At higher altitudes, R. glacialis can double the time taken for seed development but runs a high risk of seeds not maturing in time.     

Contrasting effects of warming and increased snowfall on Arctic tundra plant phenology over the past two decades

Recent changes in climate have led to significant shifts in phenology, with many studies demonstrating advanced phenology in response to warming temperatures. The rate of temperature change is especially high in the Arctic, but this is also where we have relatively little data on phenological changes and the processes driving these changes. In order to understand how Arctic plant species are likely to respond to future changes in climate, we monitored flowering phenology in response to both experimental and ambient warming for four widespread species in two habitat types over 21 years. We additionally used long‐term environmental records to disentangle the effects of temperature increase and changes in snowmelt date on phenological patterns. While flowering occurred earlier in response to experimental warming, plants in unmanipulated plots showed no change or a delay in flowering over the 21‐year period, despite more than 1 °C of ambient warming during that time. This counterintuitive result was likely due to significantly delayed snowmelt over the study period (0.05–0.2 days/yr) due to increased winter snowfall. The timing of snowmelt was a strong driver of flowering phenology for all species – especially for early‐flowering species – while spring temperature was significantly related to flowering time only for later‐flowering species. Despite significantly delayed flowering phenology, the timing of seed maturation showed no significant change over time, suggesting that warmer temperatures may promote more rapid seed development. The results of this study highlight the importance of understanding the specific environmental cues that drive species’ phenological responses as well as the complex interactions between temperature and precipitation when forecasting phenology over the coming decades. As demonstrated here, the effects of altered snowmelt patterns can counter the effects of warmer temperatures, even to the point of generating phenological responses opposite to those predicted by warming alone.     

Climate change shifts population structure and demographics of an alpine herb,Anemone narcissiflora ssp. sachalinensis (Ranunculaceae), along a snowmelt gradient

Alpine ecosystems, characterized by cold climates and short growing seasons, are thought to be most vulnerable to climate change. Warmer temperatures and earlier snowmelt extend the growing season length and increase drought stress for alpine plants, resulting in changes to their distribution. Anemone narcissiflora ssp. sachalinensis is a perennial herb that grows in the alpine snow-meadows of northern Japan. In the last few decades, its distribution has shifted toward later snowmelt habitat in the Taisetsu Mountains of Hokkaido. We recorded demographic data for this species at early, middle and late snowmelt habitats over four years (2009–2012), and constructed transition matrix models to evaluate how demographic parameters and population growth rate vary between local habitats along a snowmelt gradient. The proportion of reproductive plants was low and seed production was limited in the early snowmelt habitat, with drier soil conditions, in comparison to the middle and late snowmelt habitats, with moist soil conditions. Evidence of the transition from small plants to those in the reproductive stage was limited in the early snowmelt habitat, suggesting that growth was inhibited; the local population in this habitat was estimated to be sustained by seed migration from later snowmelt habitats. These results indicate that advancing snowmelt under climate change may decrease the reproductive activity and population growth rate of snow-meadow plants if seed migration from later snowmelt populations is limited, resulting in the extinction of local populations.     

Warming effects on growth,production, and vegetation structure of alpine shrubs: a five-year experiment in northern Japan

Warming effects on shoot growth, production, reproductive activity, and vegetation structure of alpine shrubs were measured over 5 years in a mid-latitude alpine fellfield in northern Japan. Open-top chambers (OTC) increased the daily mean air-temperature by 1.5-2.3 degrees C throughout the growing season but the effect on soil temperature was small. Two evergreen species, Ledum palustre and Empetrum nigrum, tended to increase their annual shoot production and aboveground-mass accumulation in the OTCs, whereas flower production did not differ. Two deciduous species, Vaccinium uliginosum and Arctous alpinus, increased their flower production in the OTCs, whereas the vegetative growth and mass accumulation did not change. No significant differences in vegetative and flower production were detected in Vaccinium vitis-idaea between the OTCs and control plots. The shoot survival and growth in terms of height of most species increased in the OTCs relative to the control treatment, and the growth rate was significantly different among species. As a result, interspecific competition seemed to be accelerated in the OTCs, and the less competitive V. vitis-idaea was suppressed by other plant species. The response to the warming observed in this study was rather different from that seen in arctic and subarctic plants even within the same species, indicating that the warming effect may cause different responses between arctic and mid-latitude alpine ecosystems. We concluded that the artificial warming over 5 years accelerated the growth of a few restricted species and lead to the change in vegetation structure in the mid-latitude alpine ecosystem.     

Small-scale plant species distribution in snowbeds and its sensitivity to climate change

Alpine snowbeds are characterized by a long-lasting snow cover and low soil temperature during the growing season. Both these key abiotic factors controlling plant life in snowbeds are sensitive to anthropogenic climate change and will alter the environmental conditions in snowbeds to a considerable extent until the end of this century. In order to name winners and losers of climate change among the plant species inhabiting snowbeds, we analyzed the small-scale species distribution along the snowmelt and soil temperature gradients within alpine snowbeds in the Swiss Alps. The results show that the date of snowmelt and soil temperature were relevant abiotic factors for small-scale vegetation patterns within alpine snowbed communities. Species richness in snowbeds was reduced to about 50% along the environmental gradients towards later snowmelt date or lower daily maximum temperature. Furthermore, the occurrence pattern of the species along the snowmelt gradient allowed the establishment of five species categories with different predictions of their distribution in a warmer world. The dominants increased their relative cover with later snowmelt date and will, therefore, lose abundance due to climate change, but resist complete disappearance from the snowbeds. The indifferents and the transients increased in species number and relative cover with higher temperature and will profit from climate warming. The snowbed specialists will be the most suffering species due to the loss of their habitats as a consequence of earlier snowmelt dates in the future and will be replaced by the avoiders of late-snowmelt sites. These forthcoming profiteers will take advantage from an increasing number of suitable habitats due to an earlier start of the growing season and increased temperature. Therefore, the characteristic snowbed vegetation will change to a vegetation unit dominated by alpine grassland species. The study highlights the vulnerability of the established snowbed vegetation to climate change and requires further studies particularly about the role of biotic interactions in the predicted invasion and replacement process.     

Demography of an endangered endemic rupicolous cactus

The snow cover extent is an important factor for the structure and composition of arctic and alpine tundra communities. Over the last few decades, snowmelt in many arctic and alpine regions has advanced, causing the growing season to start earlier and last longer. In a field experiment in subarctic tundra in Interior Alaska, I manipulated the timing of snowmelt and measured the response in mortality, phenology, growth, and reproduction of the eight dominant plant species. I then tested whether the phenological development of these species was controlled by snowmelt date or by temperature (in particular growing degree days, GDD). In order to expand our understanding of plant sensitivity to snowmelt timing, I explored whether the response patterns can be generalized with regard to the temporal niche of each species. Differences in the phenology between treatments were only found for the first stages of the phenological development (=phenophases). The earlier the temporal niche (i.e., the sooner after snowmelt a species develops) the more its phenology was sensitive to snowmelt. Later phenophases were mostly controlled by GDD, especially in late-developing species. In no species did an earlier snowmelt and a longer growing season directly enhance plant fitness or fecundity, in spite of the changes in the timing of plant development. In conclusion, the temporal niche of a species’ phenological development could be a predictor of its response to snowmelt timing. However, only the first phenophases were susceptible to changes in snowmelt, and no short-term effects on plant fitness were found.     

Ecological and evolutionary responses of an arctic plant to variation in microclimate and soil

The arctic and alpine regions are predicted to experience some of the highest rates of climate change, and the arctic vegetation is expected to be especially sensitive to such changes. Understanding the ecological and evolutionary responses of arctic plant species to changes in climate is therefore a key objective. Geothermal areas, where natural temperature gradients occur over small spatial scales, and without many of the confounding environmental factors present in latitudinal and other gradient studies, provide a natural experimental setting in which to examine the response of arctic–alpine plants to increasing temperatures. To test the ecological and evolutionary response of the circumpolar alpine bistort Persicaria vivipara to temperature, we collected plant material and soil from areas with low, intermediate and high soil temperatures and grew them at three different temperatures in a three-factorial growth chamber experiment. At higher experimental soil temperatures, sprouting was earlier and plants had more leaves. Sprouting was earlier in soil originating from intermediate temperature and plants had more leaves when grown in soil originating from low temperatures. We did not find evidence of local adaptation or genetic variation in reaction norms among plants originating from areas with low, intermediate and high soil temperature. Our findings suggest that the alpine bistort has a strong plastic response to warming, but that differences in soil temperature have not resulted in genetic differentiation. The lack of an observed evolutionary response may, for example, be due to the absence of temperature-mediated selection on P. vivipara, the low rate of sexual recombination, or high levels of gene flow balancing differences in selection. When placed within the context of other studies, we conclude that arctic–alpine plant species often show strong plastic responses to spring warming, while evidence of evolutionary responses varies among species.     

Plant functional traits mediate reproductive phenology and success in response to experimental warming and snow addition in Tibet

Global climate change is predicted to have large impacts on the phenology and reproduction of alpine plants, which will have important implications for plant demography and community interactions, trophic dynamics, ecosystem energy balance, and human livelihoods. In this article we report results of a 3‐year, fully factorial experimental study exploring how warming, snow addition, and their combination affect reproductive phenology, effort, and success of four alpine plant species belonging to three different life forms in a semiarid, alpine meadow ecosystem on the central Tibetan Plateau. Our results indicate that warming and snow addition change reproductive phenology and success, but responses are not uniform across species. Moreover, traits associated with resource acquisition, such as rooting depth and life history (early vs. late flowering), mediate plant phenology, and reproductive responses to changing climatic conditions. Specifically, we found that warming delayed the reproductive phenology and decreased number of inflorescences of Kobresia pygmaea C. B. Clarke, a shallow‐rooted, early‐flowering plant, which may be mainly constrained by upper‐soil moisture availability. Because K. pygmaea is the dominant species in the alpine meadow ecosystem, these results may have important implications for ecosystem dynamics and for pastoralists and wildlife in the region.     

Reproduction as a bottleneck to treeline advance across the circumarctic forest tundra ecotone

The fundamental niche of many species is shifting with climate change, especially in sub‐arctic ecosystems with pronounced recent warming. Ongoing warming in sub‐arctic regions should lessen environmental constraints on tree growth and reproduction, leading to increased success of trees colonising tundra. Nevertheless, variable responses of treeline ecotones have been documented in association with warming temperatures. One explanation for time lags between increasingly favourable environmental conditions and treeline ecotone movement is reproductive limitations caused by low seed availability. Our objective was to assess the reproductive constraints of the dominant tree species at the treeline ecotone in the circumpolar north. We sampled reproductive structures of trees (cones and catkins) and stand attributes across circumarctic treeline ecotones. We used generalized linear mixed models to estimate the sensitivity of seed production and the availability of viable seed to regional climate, stand structure, and species‐specific characteristics. Both seed production and viability of available seed were strongly driven by specific, sequential seasonal climatic conditions, but in different ways. Seed production was greatest when growing seasons with more growing degree days coincided with years with high precipitation. Two consecutive years with more growing degree days and low precipitation resulted in low seed production. Seasonal climate effects on the viability of available seed depended on the physical characteristics of the reproductive structures. Large‐coned and ‐seeded species take more time to develop mature embryos and were therefore more sensitive to increases in growing degree days in the year of flowering and embryo development. Our findings suggest that both moisture stress and abbreviated growing seasons can have a notable negative influence on the production and viability of available seed at treeline. Our synthesis revealed that constraints on predispersal reproduction within the treeline ecotone might create a considerable time lag for range expansion of tree populations into tundra ecosystems.     

Response to simulated climatic change in an alpine and subarctic pollen-risk strategist, Silene acaulis

The aim of this study was to test if early flowering species respond with increased seed production to climate warming as is predicted for late-flowering seed-risk strategists. Experimental climate warming of about 3°C was applied to two populations of the cushion-forming plant Silene acaulis (L.) Jacq. The experiment was run at one subarctic site and one alpine site for 2 years and 1 year, respectively, using open-top chambers (OTC).
The 2-year temperature enhancement at the subarctic site had a marked effect on the flowering phenology. Cushions inside the OTC started flowering substantially earlier than control cushions. Both the male and female phases developed faster in the OTCs, and maturation of capsules occurred earlier. The cushions also responded positively in reproductive terms and produced more mature seeds and had a higher seed/ovule ratio. After 1 year temperature enhancement at the alpine site there was a weak trend for earlier flowering, but there was no significant difference in seed production or seed/ovule ratio.     

Habitat-specific responses in the flowering phenology and seed set of alpine plants to climate variation: implications for global-change impacts

The timing of the snowmelt is a crucial factor in determining the phenological schedule of alpine plants. A long-term monitoring of snowmelt regimes in a Japanese alpine area revealed that the onset of the snowmelt season has been accelerated during the last 17 years in early snowmelt sites but that such a trend has not been detected in late snowmelt sites. This indicates that the global warming effect on the snowmelt pattern may be site-specific. The flowering phenology of fellfield plants in an exposed wind-blown habitat was consistent between an unusually warm year (1998) and a normal year (2001). In contrast, the flowering occurrence of snowbed plants varied greatly between the years depending on the snowmelt time. There was a large number of flowering species in the fellfield community from mid- to late to late June and from mid- to late July. The flowering peak of an early-melt snowbed plant community was in the middle of the flowering season and that of a late-melt snowbed community was in the early flowering season. These habitat-specific phenological patterns were consistent between 1998 and 2001. The effects of the variation in flowering timing on seed-set success were evaluated for an entomophilous snowbed herb, Peucedanum multivittatum, along the snowmelt gradient during a 5-year period. When flowering occurred prior to early August, mean temperature during the flowering season positively influenced the seed set. When flowering occurred later than early August, however, the plants enjoyed high seed-set success irrespective of temperature conditions if frost damage was absent. These observations are probably explained based on the availability of pollinators, which depends not only on ambient temperature but also on seasonal progress. These results suggest that the effects of climate change on biological interaction may vary depending on the specific habitat in the alpine ecosystem in which diverse snowmelt patterns create complicated seasonality for plants within a very localized area.     

Intrinsic and extrinsic factors acting on the reproductive process in alpine‐snowbed plants: roles of phenology,biological interaction,and breeding system

Pollinator activity and competition for pollinators lead to quantitative and qualitative pollen limitations on seed production and affect the reproductive success of plant species, depending on their breeding system (e.g., self‐compatibility and heterospecific compatibility) and genetic load (e.g., inbreeding depression and hybrid inviability). In alpine ecosystems, snowmelt regimes determine the distribution and phenology of plant communities. Plant species growing widely along a snowmelt gradient often grow with different species among local populations. Their pollinators also vary in their abundance, activity, and behavior during the season. These variations may modify plant–pollinator and plant–plant interactions. We integrated a series of our studies on the alpine dwarf shrub, Phyllodoce aleutica (Ericaceae), to elucidate the full set of intrinsic (species‐specific breeding system) and extrinsic factors (snow condition, pollinator activity, and interspecific competition) acting on their reproductive process. Seasonality of pollinator activity led to quantitative pollen limitation in the early‐blooming populations, whereas in the late‐blooming populations, high pollinator activity ensured pollination service, but interspecific competition for pollinators led to qualitative and quantitative pollen limitation in less competitive species. However, negative effects of illegitimate pollen receipt on seed‐set success might be reduced when cryptic incompatibility systems (i.e., outcross pollen grains took priority over self‐ and heterospecific pollen grains) could effectively prevent ovule and seed discounting. Our studies highlight the importance of species‐specific responses of plant reproduction to changing pollinator availability along environmental gradients to understand the general features of pollination networks in alpine ecosystems.     

Influence of Snowmelt Timing on the Diet Quality of Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Implications for Reproductive Success

The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing.     

Mating systems of snowbed plant species of the northeastern Calcareous Alps of Austria

Predicted climate warming will likely reduce the area and increase the fragmentation of alpine snowbed habitats. The ability of snowbed plants to cope with such fragmentation will, among other things, depend on their reproductive strategy. With respect to the mating system, as a key component of reproductive strategies, the environmental conditions in arctic and alpine snowbeds have been hypothesized to select for high selfing ability due to short growing seasons and unpredictable pollinator service. In this study we evaluate whether the mating system strategies of seven typical snowbed forbs of the northeastern Calcareous Alps in Austria are in line with this hypothesis. Field-pollination experiments were conducted in order to study the effects of pollinator exclusion (bagging; all study species), emasculation and manual self- and cross-pollination (subset of study species) on seed set. Additionally, data on floral traits associated with the reproductive system such as anther and ovule numbers and pollen:ovule ratios were collected. Results demonstrate that selfing is not uncommon but by no means obligatory for snowbed plants: the study species display a wide range of mating system types, from predominately outcrossing to predominately selfing. The different reproductive strategies of regional snowbed plants are discussed in relation to their ability to cope with climate warming induced habitat fragmentation.     

Reproductive output in Mediterranean shrubs under climate change experimentally induced by drought and warming

The effects of climate change on plant reproductive performance affects the sequence of different plant reproductive stages from flowering to seed production and viability, as well as the network of relationships between them. These effects are expected to respond to different components of climate change, such as temperature and water availability, and may be sensitive to differences in species phenology.We used long-term experimental drought and warming treatments to study the effect of climate change on flower production, fruit and seed-set, seed size and seed germination rate (proportion of germinating seeds) in three Mediterranean shrubs coexisting in a coastal shrubland.Larger plants produced significantly more flowers in all three species, and higher fruit-set in Dorycnium pentaphyllum. Flower production was reduced in drought and warming treatments in the spring-flowering species D. pentaphyllum and Helianthemum syriacum, but not in the autumn–winter species Erica multiflora, which increased flowering in the warming treatment. However, the drought treatment eventually resulted in a decreased seed-set in E. multiflora. Structural equation modelling revealed strong correlations between the sequential reproductive stages. Specifically, flower density in inflorescences determined seed-set in H. syriacum, and seed size and germination rate in E. multiflora. Nevertheless, the relevance of relationships between reproductive traits changed between climatic treatments: in D. pentaphyllum a direct relationship between plant size and seed size only arised in the drought treatment, while in H. syriacum climate treatments resulted in a stronger relationship between the number of flowers and seed-set.This experimental study shows the ability of changing climatic variables to determine the reproductive sequential process of woody species. We show that several parameters of the reproductive performance of some Mediterranean species are affected by drought and warming treatments simulating climate change, highlighting the importance of changes in both water availability and temperature, and the sequential relationship between reproductive stages. Phenological patterns also contribute to species’ differential responses to climatic change, due to the relationship of these patterns with resource availability, environmental conditions and plant–pollinator interactions.